It is well known from many actual car accidents and experimental data that wearing of seatbelts is very effective for assuring safety of drivers and passengers. For this reason the wearing of seatbelts is nowadays mandatory and the persons who fail to comply the seatbelt law are subject to penalty provisions.
However, drivers and passengers often fail or forget to wear the seatbelt mainly because of limits in freedom of their upper bodies or restrained from or troublesome operations. As a consequence, the drivers and passengers not only subject to penalties but also experience unforeseen situations with their lives when they are involved in a car accident. Any measures are needed for assuring that all drivers and passengers wear the seatbelts. It is possible to install such safety measures during design or manufacturing of vehicles. However, it is not so easy to install such safety measures in the vehicles that are already in use by consumers.
U.S. Pat. Nos. 6,215,395 and 3,693,147 show such safety devices which include a plurality of seat sensors and a plurality of seatbelt switches to activate a visual or voice alarm or stop the engine from running for forcing wearing of seatbelts by a driver and a passenger. However, the individual seat sensors and seatbelt switches in the safety devices shown by those references work separately or independently so that alarm lamps are blinking or voice alarms are generating separately or independently even if no driver sits on the driver seat and the vehicle is not ready for driving.